In the concept now most widely accepted, cancer is considered to be the result of abnormal changes within cells. Although it is admitted that the disease may have different etiologies, it is the cell which is regarded as the pathogenic entity. A group of specific changes in the cells is believed to represent the fundamental abnormality.

In today's prevailing outlook, differences between tumors are attributed to the multiple secondary characteristics present in the diseased cells along with a primary specific anomaly. The complex clinical manifestations of cancer are further explained in terms of the relationship between cancerous cells, as pathogenic entities, and the whole organism. Clinical evolution, from local innocuous process to lethal disease is related to anatomical spread of cancerous cells from their original site. Abnormal metabolic changes seen in the organism are believed to result from the influence exerted by functional abnormalities of the cancerous cells. In a still narrower view, cancer is considered to be the result of abnormality of a single specific function of the cell—its growth. Qualitatively and quantitatively, abnormal growth has been considered to be the capital factor in the pathogenesis of the disease. (292)

In contrast to this classical view, our studies have led us to regard cancer as something other than an abnormality limited to the cell alone.

As we have seen, the organism is a complex hierarchic organization of different biological entities. We sought to determine where cancer fits in this complex organization. Can cancer with its manifestations and its evolution be better understood if systematized in accordance with the hierarchical organization of the organism? Can both manifestations and evolution be related not alone to a cellular abnormality but rather to a progressive participation in the disease of the different hierarchic levels of the organism?

We have found that such participation cannot be analyzed readily in the advanced cancerous subject with so many and such varied manifestations of the disease already present. Similarly, incipient cases with a paucity of clinical manifestations are not ideal for the purpose. It was only by following the successive appearance of manifestations during the evolution of cancer that their relationship to the level of hierarchic organization involved could be clearly seen.

Identification of the level involved at each point in the development of cancer was greatiy facilitated by conceptually separating the clinical evolution of the disease into a series of successive phases and identifying the changes which characterize the passage from one phase to the next.

We have chosen to call these phases precancerous, noninvasive, invasive, painful, preterminal and terminal. We will briefly identify them and their salient features here.